1. Field of the Invention
The present invention relates to diagnostic imaging inside the human body. In particular, the present invention relates to obtaining images of the digestive tract using capsule endoscopy.
2. Discussion of the Related Art
Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that pass into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is formed at the distal end using a lens and transmitted to the proximal end, outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. A conceptually similar instrument might record an image electronically at the distal end, for example using a CCD or CMOS array, and transfer the image data as an electrical signal to the proximal end through a cable. Endoscopes allow a physician control over the field of view and are well-accepted diagnostic tools. However, they do have a number of limitations, present risks to the patient, are invasive and uncomfortable for the patient, and their cost restricts their application as routine health-screening tools.
Because of the difficulty traversing a convoluted passage, endoscopes cannot reach the majority of the small intestine and special techniques and precautions, that add cost, are required to reach the entirety of the colon. Endoscopic risks include the possible perforation of the bodily organs traversed and complications arising from anesthesia. Moreover, a trade-off must be made between patient pain during the procedure and the health risks and post-procedural down time associated with anesthesia. Endoscopies are necessarily inpatient services that involve a significant amount of time from clinicians and thus are costly.
An alternative in vivo image sensor that addresses many of these problems is capsule endoscope. A camera is housed in a swallowable capsule, along with a radio transmitter for transmitting data, primarily comprising images recorded by the digital camera, to a base-station receiver or transceiver and data recorder outside the body. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead of radio-frequency transmission, lower-frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule.
An early example of a camera in a swallowable capsule is described in U.S. Pat. No. 5,604,531. Other patents, such as U.S. Pat. Nos. 6,709,387 and 6,428,469, describe more details of such a system, using a transmitter to send the camera images to an external receiver. Still other patents, including U.S. Pat. No. 4,278,077, describe similar technologies. For example, U.S. Pat. No. 4,278,077 shows a capsule with a camera for the stomach, which includes film in the camera. U.S. Pat. No. 6,939,292 shows a capsule with a buffering memory, a timer, and a transmitter.
One advantage of an autonomous encapsulated camera with an internal battery is that measurements may be made with the patient ambulatory, out of the hospital, and with moderate restriction of activity. The base station includes an antenna array surrounding the bodily region of interest and this array can be temporarily affixed to the skin or incorporated into a wearable vest. A data recorder is attached to a belt and includes a battery power supply and a data storage medium for saving recorded images and other data for subsequent uploading onto a diagnostic computer system.
A typical procedure consists of an inpatient visit in the morning during which a clinician attaches the base station apparatus to the patient and the patient swallows the capsule. The system records images beginning just prior to swallowing and records images of the gastrointestinal (GI) tract until its battery becomes fully discharged. Peristalsis propels the capsule through the GI tract. The rate of passage depends on the degree of motility. Usually, the small intestine is traversed in 4 to 8 hours. After a prescribed period, the patient returns the data recorder to the clinician who then uploads the data onto a computer for subsequent viewing and analysis. The capsule is passed in time through the rectum and need not be retrieved.
The capsule camera allows the GI tract from the esophagus down to the end of the small intestine, especially the small intestine, to be imaged in its entirety, although it is not optimized to detect anomalies in the stomach. Color photographic images are captured so that anomalies can be detected even when only small visually recognizable characteristics, not topography, are available. The procedure is pain-free and requires no anesthesia. Risks associated with the capsule passing through the body are minimal—certainly, the risk of perforation is much reduced relative to endoscopy. The cost of the procedure is also less than for an endoscopy due to the decreased use of clinician time and clinic facilities, and the absence of anesthesia.
Despite these advantages, the existing capsule camera solutions have limitations as well. Although the base station and data recorder are designed to minimize discomfort and maximize mobility, they necessarily hamper the patient during the measurement and create discomfort. Also, sleeping with the apparatus attached would be difficult, necessitating that the measurement commence and finish during waking hours. The cost of the procedure is not sufficiently low to allow the procedure to become a routine screening procedure. The time required for a clinician to attach the antenna array and the data recorder is a significant contributor to the total cost. The costs of the data recorders and the base stations become significant as the number of patients concurrently measured increases beyond one or two. Also, the radio transmitter in the capsule, which includes an antenna, is a significant contributor to its cost, size, and power consumption. The radio link, then, is responsible, directly and indirectly, for much of the cost. The wireless system may also suffer radio interference from MRI, airport security devices, amateur video systems, or other sources of RF radio signal in the spectrum. There may also be interference between this system and other implant devices, either within a single patient or between two nearby persons. Another significant factor contributing to cost is the doctor's time for viewing the images. In current devices, such images may number in many thousands, which adds to patient history archiving cost and presents an obstacle for internet transmission of such data.
Another limitation of the current solutions is their inability to reliably image the colon. The colon presents a number of challenges for the imaging system. A number of complications arise because the capsule takes longer to pass through the entire GI tract than just through the small intestine. In fact, ingested material can easily take 24 hours or longer to pass through the colon, although this time can be reduced with motility-enhancing drugs. Imaging the colon with an existing system would thus require the patient to wear the base station, including the antenna array, and the data recorder for a longer period of time.
The increased measurement time leads to logistical complications. The colon must be purged prior to imaging and remain free of digested or partially-digested food which would obscure the colon wall from the camera. Any beverages, such as fruit juices or sodas, that are metabolized by bacteria in the colon will thereupon become turbid. Thus, if an autonomous capsule taken orally is to image the colon, the patient must refrain from eating or drinking fluids (except water) for approximately a period lasting at least from the time the purgative is consumed until the time the capsule is passed (minus the minimum time taken for the digested food or beverage to reach the camera in the colon). Even with the aid of motility-enhancing drugs, the fast must persist for at least eight hours after the capsule is swallowed, as compared to just a few hours for imaging of the small intestine alone. Additional restrictions on the timing of the measurement arise from the practical requirement that the data recorder and the antenna array be attached during normal office hours and by the fact that sleeping with the apparatus attached would be difficult. All of these logistical constraints make it difficult to design a protocol which is convenient for both patients and clinicians, which minimizes the discomfort of fasting, and which maximizes the number of patients that one clinic or clinician can test.
U.S. Pat. No. 6,800,060 describes a swallowable data-recorder capsule that may be retrieved after passing from the body. However, this system specifies an expensive and rare ultra-high-density atomic-resolution storage (ARS) medium. U.S. Patent Application Publication US2005/0183733 shows a capsule with a balloon that is deployed depending on positional information.